The present invention relates to second gas barrier which prevents the leakage of gas by being used for a liquefied natural gas (LNG) and other gas storage tanks. Gases such as LNG have the risk of explosion when it leaks out of the gas storage tank, and in particular, the LNG liquefaction temperature is less than or equal to 163° C. The conventional LNG storage tank is composed of a first gas barrier, a heat insulating material, and a second gas barrier, in order to prevent the leakage of gas in a more stable manner in the adverse conditions of below 163° C. Since second barrier must have the characteristic of being able to prevent gas leakage secondarily in case of the primary barrier damage, it is one of the important materials used for LNG storage tanks.
The background technology for the present invention is KR 10-2013-0050837 (Patent Document 1). The above mentioned background art provides a flexible second gas barrier for liquefied gas storage tank, wherein the adhesive strength is improved and the mechanical properties is strengthened by using an aluminum foil which has undergone physical and chemical treatments on both sides, for the improvement of flexibility and adhesive strength, and also, wherein the thermal stability is ensured and the tensile strength is improved by using an urethane elastomer as an adhering sheet on the stiffener fabric made of a glass fiber.
Recently, LNG ship cargo is further enlarged, and as the thickness of LNGC Foam becomes thicker in order to improve the BOR performance, which is a loss rate of LNG during voyage, the repeated load according to the displacement which is imposed on the second gas barrier is also on the increases, and in conventional technology, there was a limit to solve the problems associated with repeated load increase imposed on second gas barrier under cryogenic conditions. Therefore, there was a need to improve the fatigue resistance of the second gas barrier.